Trailers are commonly used for the transportation of goods. A trailer is generally attached to and pulled by a powered vehicle such as a car or, for a larger trailer, a tractor truck.
Typically, the mounting of wheels on a trailer frame can be accomplished by fixing a wheel at each end of a rotating axle which is then mounted under the frame of the trailer, or by mounting each wheel on separate fixed spindles on each side of the vehicle, the wheel rotating around the fixed axle.
In both cases, the wheels are always oriented parallel to the frame. This configuration is adapted to the trailer traveling in a straight line, but is problematic when the trailer is negotiating a curve. In that instance, the wheels become unaligned with the trajectory of the trailer during the turn, resulting in wheels of the trailer slipping on the road.
It is therefore desirable to be able to orient the wheels to keep the wheels aligned (i.e. tangential) with the trajectory of the trailer. Moreover, in a turn, the wheels on each side of a vehicle do not follow the same trajectory. For instance, when negotiating a left turn, the wheels on the right side of the trailer follow a curved trajectory having a radius of curvature greater than the wheels on the left side of the trailer. Therefore, the wheels on either side of the trailer will slip during the turn, causing premature wear to the tires mounted on the wheels and possibly leading to serious accidents.
In hopes of overcoming such drawbacks, some apparatuses for orienting wheels on a trailer have been proposed. In one such apparatus, the wheels are mounted on an axle and are linked using a rack-and-pinion system, which is widely used in modern cars and therefore well-known in the art. Unfortunately, this system does not allow the wheels on the left and right side of the trailer to be turned at different angles and therefore does not solve the wheel slippage problem.
Further, the laws of most jurisdictions define a maximum distance between the wheels on the left side and on the right side of the vehicle. The wheels are therefore required to be positioned relatively close to the frame of the trailer. This configuration thus prevents the wheels from turning to great angles without contacting the trailer frame.
Another apparatus consists of a dolly or bogie system being pivotally mounted under the trailer. A dolly comprises a chassis mounted on a set of wheels, generally linked together by a rigid axle. While the wheels remain parallel to the dolly at all time, the whole dolly can pivot in relation to the trailer when the trailer negotiates a turn. Once again, because this system lacks the ability to orient wheels on the left side and the right side at the vehicle at different angles, the slippage issue is not resolved. Further, the installation of a dolly under the trailer raises the overall center of mass of the trailer, which then increases the risk of the trailer tipping over when turning.
Other apparatuses involving complex hydraulic circuits have been proposed, but are often too complicated, cumbersome and are prone to leaks, which would be most undesirable, especially if the trailer is traveling at great speed.
There is therefore a need for an apparatus that will overcome at least one of the above-identified drawbacks.
Features of the invention will be apparent from review of the disclosure, drawings and description of the invention below.